Improve status banner GUI

[ROpdebee]

The current status banner of ECAU only shows the most recent message. It should be replaced by a nicer GUI which retains the previous messages as well, similar to the ones in the work code paster.

[ROpdebee]

We should also sprinkle some more logging messages in the image fetcher. I did a quick test with a Discogs release with 28 images, it was taking a long time to complete without any status updates (likely because of #71), but adding at least a message per image that is fetched would be good. Those message should probably be transient though, solely to indicate progress but not persisted in the "history" of the status banner.